Paul P. Breen

A pilot evaluation of a neuromuscular electrical stimulation (NMES) based methodology for the prevention of venous stasis during bed rest

Bed rest poses an increased risk factor for a potentially fatal venous thromboembolism (VTE). Lack of activation of the calf muscle pump during this resting period gives rise to venous stasis which may lead to deep vein thrombosis (DVT) development. Our aim was to investigate the effects that 4h of bed rest have on the lower limb hemodynamics of healthy subjects and to what extent electrically elicited contractions of the calf muscles can alleviate these effects. Outcome variables included popliteal vein blood flow and heart rate. Primary results indicated that the resting group experienced a significant decline in popliteal venous blood flow of approximately 47% with approximately 13% decrease in heart rate. The stimulated groups maintained a significantly higher venous blood flow and heart rate. Volume flow in the contralateral limb remained constant throughout the study and was comparable to that of the stimulated limbs recovery flow. The results suggest that even short periods of bed rest can significantly reduce lower limb blood flow which could have implications for DVT development. Electrically elicited calf muscle contractions significantly improve lower limb blood flow and can alleviate some debilitating effects of bed rest.

BION microstimulators : A case study in the engineering of an electronic implantable medical device

The BION (Bionic Neuron) is a single channel implantable neurostimulator of unique design that can be delivered by injection. The development of the BION injectable neurostimulators exemplifies a challenging, but well posed medical design problem addressed with a successful strategy for prioritizing and resolving the biomedical and technological challenges. Though some performance requirements required post-evaluation revision, all fundamental goals were realized. A small number of significant design corrections occurred because the device requirements did not include the full scope of environmental demands. The design has spawned a number of variants optimized for diverse biomedical applications, and its clinical applications continue to evolve. The BION development history demonstrates design successes worth emulating and design pitfalls that may be avoidable for future medical device development teams. This paper serves as an introduction to the BION microstimulator technology and as an analysis of the design process used to develop the early clinical devices.

A programmable and portable NMES device for drop foot correction and blood flow assist applications

The Duo-STIM, a new, programmable and portable neuromuscular stimulation system for drop foot correction and blood flow assist applications is presented. The system consists of a programmer unit and a portable, programmable stimulator unit. The portable stimulator features fully programmable, sensor-controlled, constant- voltage, dual-channel stimulation and accommodates a range of customized stimulation profiles. Trapezoidal and free-form adaptive stimulation intensity envelope algorithms are provided for drop foot correction applications, while time dependent and activity dependent algorithms are provided for blood flow assist applications. A variety of sensor types can be used with the portable unit, including force sensitive resistor based foot switches and NMES based accelerometer and gyroscope devices. The paper provides a detailed description of the hardware and block-level system design for both units. The programming and operating procedures for the system are also presented. Finally, functional bench test results for the system are presented.

Electronic stimulators for surface neural prosthesis

This paper presents the technological advancements in neural prosthesis devices using Functional Electrical Stimulation (FES). FES refers to the restoration of motor functions lost due to spinal cord injury (SCI), stroke, head injury, or diseases such as Cerebral Palsy or Multiple Sclerosis by eliciting muscular contractions through the use of a neuromuscular electrical stimulator device. The field has developed considerably since its inception, with the miniaturisation of circuity, the development of programmable and adaptable stimulators and the enhancement of sensors used to trigger the application of stimulation to suit a variety of FES applications. This paper discusses general FES system design requirements in the context of existing commercial and research FES devices, focusing on surface stimulators for the upper and lower limbs. These devices have demonstrated feasible standing and stepping in a clinical setting with paraplegic patients, improvements in dropped foot syndrome with hemiplegic patients and aided in the restoration of grasping function in patients with upper limb motor dysfunction.

Patient tolerance of neuromuscular electrical stimulation (NMES) in the presence of orthopaedic implants

Neuromuscular electrical stimulation (NMES) may help reduce the incidence of deep vein thrombosis (DVT) in the postoperative total hip and knee arthroplasty patient. However, discomfort associated with stimulus may reduce patient acceptance of NMES as therapy. The aim of this study was to determine if patient comfort and tolerance of NMES was affected by applying stimulation in proximity to an orthopaedic implant. There was a concern that this may cause a concentration of current around the metal which could result in hypersensitivity of NMES and reduce its effectiveness. Twenty patients took part in this study, 10 total hip and 10 total knee arthroplasty patients. Each patient was at least 3 weeks post surgery. NMES was applied to the calf muscles of each leg using skin surface electrodes. Four excitatory levels were recorded, which were: sensory threshold, motor threshold, pain threshold and pain tolerance. Following this, patients underwent a 5 min stimulation session and indicated their overall comfort level on a visual analogue scale. Measurements of peak venous velocity, mean velocity and volume flow were recorded by duplex scanning from the popliteal vein at rest and in response to NMES elicited contractions during this session. Finally, patients completed a short verbal interview detailing their experience with the NMES treatment. The blood flow results showed increases in peak venous velocities, mean velocities and volume flow produced by NMES of 200%, 60% and 60% respectively when compared to resting blood flow. Comfort assessment indicated that the presence of a metallic implant did not give rise to hypersensitivity due to NMES. Patients found the application of calf muscle NMES comfortable and acceptable as a treatment. We conclude that the use of NMES on postoperative orthopaedic patients can be safely administered as a DVT prevention method.

Extending the viability of acute brain slices

The lifespan of an acute brain slice is approximately 6–12 hours, limiting potential experimentation time. We have designed a new recovery incubation system capable of extending their lifespan to more than 36 hours. This system controls the temperature of the incubated artificial cerebral spinal fluid (aCSF) while continuously passing the fluid through a UVC filtration system and simultaneously monitoring temperature and pH. The combination of controlled temperature and UVC filtering maintains bacteria levels in the lag phase and leads to the dramatic extension of the brain slice lifespan. Brain slice viability was validated through electrophysiological recordings as well as live/dead cell assays. This system benefits researchers by monitoring incubation conditions and standardizing this artificial environment. It further provides viable tissue for two experimental days, reducing the time spent preparing brain slices and the number of animals required for research.

Hemodynamic effects of habituation to a week-long program of neuromuscular electrical stimulation

OBJECTIVES Neuromuscular electrical stimulation (NMES) of the calf muscles has been shown to cause instantaneous increases in venous outflow from the lower leg and could be used as an adjunct to current gold-standard compression therapies for the prevention of venous stasis and its related pathologies. However, little is known about the effects of NMES in combination with compression therapies on subject comfort, compliance and popliteal venous blood flow over the course of a week-long NMES protocol. This study aimed to assess the effects of a NMES and compression protocol for the prevention of venous stasis on the compliance, comfort and venous blood flow of healthy volunteers over the course of seven days. DESIGN Twenty-four healthy subjects were assigned to either a stimulation or control group. The stimulation group received 1.5 h of NMES daily while the control group received none. Daily measures of popliteal venous blood flow, subject compliance and comfort were recorded over 7 days. RESULTS Ejected blood flow volumes and peak velocities in the popliteal vein during NMES were sustained over a 30-min stimulation session and increased by approximately 100% over the course of seven days. Mean stimulation intensities increased progressively throughout the week, while perceived pain during NMES decreased significantly. Mean compliance to the 7-day protocol was 100%. CONCLUSION User habituation to a combined NMES and compression protocol resulted in significant increases in ejected venous volume and peak velocity over the course of 7 days. This resulted in the highest ejected venous volume reported from a single NMES induced contraction of the calf muscles to date which was twice the magnitude of values previously reported in the literature. These findings suggest that NMES based protocols applied over an extended period of days, weeks or months may provide greater hemodynamic effect for the prevention of venous stasis than previously observed during NMES sessions lasting less than a few hours.

Venous emptying from the foot: influences of weight bearing, toe curls, electrical stimulation, passive compression, and posture.

This study investigated the hemodynamic properties of the plantar venous plexus (PVP), a peripheral venous pump in the human foot, with Doppler ultrasound. We investigated how different ways of introducing mechanical changes vary in effectiveness of displacing blood volume from the PVP. The contribution of the PVP was analyzed during both natural and device-elicited compressions. Natural compressions consisted of weight bearing on the foot and toe curl exercises. Device-elicited compressions consisted of intermittent pneumatic compression (IPC) of the foot and electrically elicited foot muscle contractions. Ten healthy participants had their posterior tibial, peroneal, anterior tibial, and popliteal vein blood flow monitored while performing these natural and device-elicited compressions of the PVP supine and in an upright position. Results indicated that 1) natural compression of the PVP, weight bearing and toe curls, expelled a significantly larger volume of blood than device-elicited PVP compression, IPC and electrical stimulation; 2) there was no difference between the venous volume elicited by weight bearing and by toe curls; 3) expelled venous volume recorded at the popliteal vein under all test conditions was significantly greater than that recorded from the posterior tibial and peroneal veins; 4) there was no significant difference between the volume in the posterior tibial and peroneal veins; 5) ejected venous volume recorded in the upright position was significantly higher than that recorded in the supine position. Our study shows that weight bearing and toe curls make similar contributions to venous emptying of the foot.

The Anatomy and Physiology of the Venous Foot Pump

The presence of a venous pumping mechanism in the foot may be significant for venous return in the lower extremities. However, there has been a lack of conclusive research in the area to date and controversy still exists over the detailed anatomy and physiologic mechanism of the venous foot pump. A full understanding of the anatomy and physiology of the venous foot pump is essential for designing effective interventions for the prevention, treatment, and management of venous disease in the lower limbs. This article highlights and discusses the relevant literature relating to the anatomy and physiology of the venous foot pump. In addition, the plantar aspects of 10 cadaveric feet were dissected. These dissections revealed the presence of a previously unreported secondary deep plantar arch and/or deep system of venous connections in the foot and facilitated a more detailed description of the patterns of doubling and branching of the primary veins of the foot. The results of these dissections are discussed within the context of previous work in the field with the aid of detailed diagrams of the dissected feet and may provide a backdrop for the physiology of the venous foot pump and its potential role in lower limb circulation. This is discussed in the last section of the article, which also highlights existing controversy regarding the role of weight bearing and muscular contraction as the dominant mechanisms for venous pumping in the foot. Anat Rec, 2010.

Evaluation of a single accelerometer based biofeedback system for real-time correction of neck posture in computer users

The worldwide adoption of computers is closely linked to increased prevalence in neck and shoulder pain. Many ergonomic interventions are available; however, the lifetime prevalence of neck pain is still estimated as high as 80%. This paper introduces a biofeedback system using a novel single accelerometer placement. This system allows the user to react and correct for movement into a position of bad posture. The addition of visual information provides artificial proprioceptive information on the cranial-vertebral angle. Six subjects were tested for 5 hours with and without biofeedback. All subjects had a significant decrease in the percentage of time spent in bad posture when using biofeedback.